Method for automatically determining the position of the front and rear wheels of a motor vehicle

ABSTRACT

The invention relates to a method for automatically determining the position of the wheels of a motor vehicle ( 10 ), characterised in that it consists in:—measuring ( 21 ) the temperature of each wheel ( 12 ) of the vehicle; and determining ( 23 ) the position of the wheels on the vehicle according to the temperature measured. The invention also relates to a corresponding position-finding device. The device is particularly suitable for monitoring the pressure inside tires.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the 35 USC 371 national stage of international applicationPCT/EP02/02237 filed on Mar. 1, 2002, which designated the United Statesof America.

FIELD OF THE INVENTION

The present invention relates to a procedure for automatically locatingthe wheels of a motor vehicle. More particularly, but not exclusively,such a procedure is associated with a tire pressure monitoring system.

BACKGROUND OF THE INVENTION

In point of fact it is already known to permanently monitor tirepressures of a vehicle. These pressure measurements (possibly correctedfor the temperature and the aging of the tire or for any otherparameter) are processed by a computer. A warning signal is emitted whena tire pressure is abnormal. The computer that processes the pressuremeasurements may be fitted onto the wheel itself or at any appropriatepoint in the vehicle.

The pressure measurements are carried out by a specific sensorassociated with each wheel. This sensor sends, to a remote computer, thepressure measurement associated with a code that identifies the sensor.Of course, it is necessary for the computer to know how to assign aposition on the vehicle to this identifying code. Thus, afterprocessing, the computer must be capable of stating that the pressuremeasurement associated with the identifying code X comes from the rightfront wheel (for example). To do this, it is necessary for the computerto learn the position of the sensor and its identifying code.

This learning may be carried out manually. For example, the computer isplaced in learning mode and requests the codes of each pressure sensorin a pre-established order. However, this learning procedure isrelatively slow and must also be repeated each time a tire is changed.It has the drawback of requiring the driver to input data into thevehicle's computer. If the driver forgets to store the new code after atire change, there is a risk of an error regarding the position of awheel with abnormal pressure. This may have serious consequences.

It would seem opportune to automatically carry out this learningprocedure during running of the vehicle. In particular, it is alreadyknown to correlate a radiofrequency signal from the sensors with a wheelposition, or else to position, close to each wheel,low-frequency/radiofrequency antennas that, by two-way communication,make it possible to identify the position of the wheels, etc.

However, these various automatic wheel-position learning methods havethe drawback that they require a complex and expensive architecture tobe installed (antennas close to the wheels, two-way communication) ormathematical processing that is very complicated and difficult to makereliable (correlation between power of the radiofrequency signal and thewheel position.

SUMMARY OF THE INVENTION

The object of the present invention is to make a correlation between thesensor identifier and its position on the vehicle in an automatic,simple and reliable manner.

For this purpose, the present invention relates to a procedure forautomatically locating the wheels of a motor vehicle, characterized inthat it consists in:

-   -   measuring the temperature of each wheel of the vehicle; and    -   determining the position of the wheels on the vehicle according        to the temperature measured.

Thus, the position of a sensor on a vehicle is simply detected accordingto the temperature (and/or the change in temperature) that it measures.This is because, for example in the case of a front wheel drive vehicle,it has been noticed that the front wheels either heat up more rapidlythan the rear wheels or they exhibit greater temperature variations.

Advantageously, the most rapid temperature variations are attributed tothe wheels located on the front axle.

However, the procedure according to the invention is not limited todetermining the front and rear wheel positions. This is because it isalso possible to determine the position of the left and right wheels inthe same way.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will emerge from the followingdescription, given by way of non-limiting example and with reference tothe appended drawings in which:

FIG. 1 is a schematic view showing the positioning of the elements ofthe device according to the invention on a motor vehicle;

FIG. 2 is a schematic diagram showing the temperature changes in thetires according to their position on the vehicle; and

FIG. 3 is a logic diagram representing the procedure according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the embodiment shown in FIG. 1, a motor vehicle 10, movingin the direction of the arrow F (FIG. 1), is provided with a system formonitoring the pressure of the tires 12. For this purpose, each tire 12is provided with a pressure sensor 11, designed to send a message to aprocessing unit 13. This message comprises, firstly, a code thatidentifies the sensor 11 and, secondly, a series of data, for examplepressure and temperature measurements.

The front axle of the vehicle bears the reference A₁ (FIG. 1) and therear axle A₂.

The processing unit 13 analyses the data received and determines whetheror not the pressure is normal. If the pressure is abnormal, a warningsignal is sent to the driver 14. The processing unit also determines theposition of the wheel on the vehicle according to the identifying codeof the sensor that has sent the message.

Of course, in order for the processing unit to be able to associate aposition on the vehicle with a sensor-identifying code, this associationmust be taught to the computer.

Within the context of the present invention, this identifyingcode/position of the sensor on the vehicle association is performedautomatically, for example each time the car is started.

In this regard, it has been noted (FIG. 2) that the temperature of eachtire differs according to its position on the vehicle. In particular,for example, during braking BR, for a front wheel drive vehicle movingat a constant speed, the front wheels A₁ exhibit a higher temperaturerise (average of the temperatures of the front wheels) than the rearwheels A₂ (average of the temperatures of the rear wheels). One of theheat sources for the tire is, in fact, the rim. The temperature of thetire therefore depends on the variation in the temperature on the rim.Now, during braking, the heat-up of the rims due to the friction of thebrakes will be greater at the front than at the rear. Consequently, inthe case of braking, the front wheels will be subjected to a greatertemperature rise than the rear wheels. The use of this informationallows us to differentiate the tires of the front axle from those of therear axle.

In the absence of braking, the main heat source for the tires is thetransmission of the drive torque to the road. Consequently, the set ofwheels that heats up the most is that on the drive axle.

The same applies in the case of the right and left tires, which, whenturning, undergo different temperature rises.

The procedure according to the invention (FIG. 3) consists in:

-   -   a) detecting the occurrence of braking 20. This braking        (indicated schematically by the driver's foot 14 pressing on a        brake pedal) is one of the data usually delivered to the        processing unit 13;    -   b) measuring, 21, the temperature within each tire, the speed S        of movement of the vehicle and the steering wheel angle α, and        taking into account the type of drive axle da (front or rear);    -   c) determining, 22, the temperature variation ΔT between two        times t₁ and t₂ (FIG. 2); and    -   d) if the temperature variation ΔT exceeds, 23, a certain        threshold Thr, then the temperature measured corresponds to a        front tire 24, otherwise it corresponds to a rear tire 25.

The temperature variation ΔT between two times t₁ and t₂ may bedetermined in several ways. For example, it is possible to make:

-   -   a comparison of the derivatives of the type:        ${\frac{\mathbb{d}T}{\mathbb{d}t} > {0\quad{and}\quad\frac{\mathbb{d}T_{1}}{\mathbb{d}t}} > \frac{\mathbb{d}T_{2}}{\mathbb{d}t}};$        T₁ being the temperature at time t₁ and T₂ the temperature at        time t₂ in the same tire;    -   or a comparison of the difference of the type:        ${\frac{\mathbb{d}\left( {T_{1} - T_{2}} \right)}{\mathbb{d}t} > 0};$    -   or else a comparison of the integrals of the type:        ∫_(t₁)^(t₂)T₁   × 𝕕t > ∫_(t₁)^(t₂)T₂   × 𝕕t;    -   or else a comparison of the values of the type T₁>T₂.

Whatever determination procedure is used, if the temperature variationdetermined is greater than a threshold Thr, the corresponding wheels arethe front wheels (in the case of front wheel drive) and vice versa inthe case of rear wheel drive. This threshold Thr is determined on a testbed for each type of vehicle.

When the speed of the vehicle is constant, the highest temperaturevalues are in fact considered as belonging to the same axle. If thevehicle has front wheel drive, this axle is the front axle A₁.

Likewise, the sensors measuring the most rapid temperature variationsare considered as belonging to the same axle (front axle).

In the example described, the procedure according to the invention alsomakes it possible to determine the position of the right and leftwheels. This is because the right and left wheels have differenttemperatures, for example when turning. Knowing the direction ofrotation of turning (for example, the steering wheel angle), it is thenpossible to determine the position of the right and left wheels. Byanalysing the steering wheel angles α, in the case of a larger angle onone side (for example on the left because of traffic circles), anunsymmetrical temperature rise between the right side and the left sideis detected.

The procedure according to the invention therefore consists in making afront/rear identification and a right/left identification of the wheelson one and the same axle, in combination with an analysis of thesteering wheel angles α and the temperature changes. Thus, each wheel ofthe vehicle is identified.

The procedure according to the invention is carried out automatically ateach startup. Once the position of the sensors is acquired withcertainty, the identification procedure according to the invention isinterrupted.

It is also possible to arrange for the procedure according to theinvention to be interrupted after a predetermined delay (for example 15min) and for a position to be assigned to each sensor on the vehicle.

The present invention also relates to a system for automaticallylocating the wheels of a motor vehicle 10, of the type comprising anumber of pressure sensors 11 each placed on a wheel 12 of the vehicleand transmitting, to a central processing unit 13, the pressure valuesmeasured in each wheel, and an identifier specific to each sensor. Thesepressure sensors also measure the temperature T within each wheels andtransmit the measured values to the central processing unit 13. Thecentral processing unit being designed to determine the location of eachwheel according to the temperatures measured.

Of course, the present invention is not limited to the embodimentdescribed above. Thus, the procedure according to the invention may becarried out when the vehicle has already traveled a certain distance (orafter a time delay) so as to wait until the temperature differencesbetween front and rear (or right and left) wheels have been properlyestablished.

1. A process for automatically locating the wheels (12) of a motorvehicle (10), comprising: measuring the steering angle of each wheel;measuring (21) the temperature of each wheel of the vehicle; anddetermining (23) the position of the wheels on the vehicle according tothe temperature measured, wherein, the temperature is measured usingsensors (11), and, the temperature sensors (11) measuring the most rapidtemperature variations are identified as belonging to the same axle. 2.The automatic location process as claimed in claim 1, wherein,when thespeed of the vehicle is constant, the temperature sensors (11) measuringthe highest temperature values are considered as belonging to the sameaxle of the vehicle.
 3. The process as claimed in claim 2, characterizedin that, when the vehicle has front wheel drive, the sensors measuringthe highest temperatures are identified as belonging to the front axle(A₁).
 4. The process as claimed in claim 1, characterized in that, afterprolonged braking, the sensors measuring the most rapid temperaturevariations are identified as belonging to the front axle.
 5. Theautomatic location process as claimed in claim 1, characterized in thata temperature variation (ΔT) is established by comparison of at leastone of the derivatives (22 a) of the temperature measured for eachwheel, the difference (22 b) of the temperatures measured for eachwheel, and the time integral (22 c) of the temperatures measured foreach wheel.
 6. The process as claimed in claim 1, characterized in thatthe step of measuring (21) the temperature of each wheel of the vehicleis carried out continuously, each time the vehicle is started.
 7. Theprocess as claimed in claim 1, characterized in that, after apredetermined time delay has elapsed, the temperature measurements areinterrupted and a position on the vehicle is assigned to each sensor. 8.A process for automatically locating the wheels (12) of a motor vehicle(10), comprising: measuring the steering angle of each wheel; measuring(21) the temperature of each wheel of the vehicle; determining (23) theposition of the wheels on the vehicle according to the temperaturemeasured; and determining a front/rear location and a right/leftlocation wheel of the same axle, by combining an analysis of thesteering wheel angles and the changes in the temperature.
 9. The processas claimed in claim 8, wherein the step of measuring the temperature ofeach wheel of the vehicle is carried out continuously, each time thevehicle is started.
 10. The process as claimed in claim 8, characterizedin that, after a predetermined time delay has elapsed, the temperaturemeasurements are interrupted and a position on the vehicle is assignedto each sensor.